Lesson 12	File test (-X) operators
Objective	Create a program that reports file information.

File Test (-X) Operators

Perl has a number of operators for testing the conditions of files. These operators are useful if you want to know if a file is readable, or executable, or if it's a directory, and so on. Because Perl was designed and written on Unix, you will find that many of these operators do not work as expected on Windows NT or other non-Unix operating systems. If you are using a non-Unix system and are unsure whether a particular operator does what you expect, you can try it from the command line with something like this:

perl -e "print -X 'filename' ? qq(true\n)
: qq(false\n)"

The example above would normally appear on a single line. It is broken into multiple lines for readability.

Here are all the file test operators defined in Perl 5, and some

Perl 5 File Test Operators

Operator	Used for
`-r`	File is readable by effective uid/gid.
`-w`	File is writable by effective uid/gid.
`-x`	File is executable by effective uid/gid.
`-o`	File is owned by effective uid.
`-R`	File is readable by real uid/gid.
`-W`	File is writable by real uid/gid.
`-X`	File is executable by real uid/gid.
`-O`	File is owned by real uid.
`-e`	File exists.
`-z`	File has zero size.
`-s`	File has nonzero size (returns size).
`-f`	File is a plain file.
`-d`	File is a directory.
`-l`	File is a symbolic link.
`-p`	File is a named pipe (FIFO).
`-S`	File is a socket.
`-b`	File is a block special file.
`-c`	File is a character special file.
`-t`	Filehandle is opened to a tty.
`-u`	File has setuid bit set.
`-g`	File has setgid bit set.
`-k`	File has sticky bit set.
`-T`	File is a text file.
`-B`	File is a binary file (opposite of -T).
`-M`	Age of file in days when script started.
`-A`	Same for access time.
`-C`	Same for inode change time.

Operator Testing

Use the operator you are testing and a suitable filename, in place of -X and filename above. Then you can see if you get the result you expect.

Common uses for file test Operators in Perl
To see if a file exists, you can check it with -e, like this:

if(-e $filename) {
 print "$filename is there!\n"
}
else {
 print "I didn't find $filename!\n"
}

Is the file a directory? Check it like this:

if(-d $filename) {
 print "$filename is a directory\n"
}
else {
 print "$filename is not a directory\n"
}

You can use the special filehandle _ to check the same file more than once. This code checks to see if a file is a plain file, then reports its size:

if(-f $filename) { 
  $size = -s _; 
  print "$filename is $size bytes." 
}
else {
  print "didn't find $filename\n"
}

Perl 6

Using String Operators

As mentioned, the difference between Perlâs functions and operators is a bit vague at times, but for convenience, the punctuation bits are referred to as operators.

Repetition Operator: x
```
STRING x INTEGER
(STRING) x INTEGER
```
The x operator is for repetition. Itâs often used to repeat a string several times:
```
my $santa_says = 'ho' x 3.7;
print $santa_says;
```
The previous code assigns hohoho to $santa_says.
Sometimes you will want to assign a single value multiple times to a list. Just put the string in parentheses to force list context:
```
my $ho = 'ho';
my @santa_says = ($ho) x 3;
```
@santa_says now contains the three strings ho, ho, and ho.

XOP Exercise

Click the Exercise link below to practice using file test operators.
XOP Exercise